Data released by WaterAid shows that about 650 million people, or one in ten of the world's population, do not have access to safe drinking water, putting them at risk of infectious diseases and premature death.

Papua New Guinea, where 60% of the population live without a safe water supply, is the most difficult and expensive place in the world to access clean water, according to a study released by WaterAid.

The study found that people in Papua New Guinea are forced to spend more than half their income on accessing water. In Port Moresby, a day's wages can be as little as $5.22 per day, a day's worth of water (13.2 gal) costs $2.67.

Equatorial Guinea, Angola, Chad and Mozambique joined Papua New Guinea in the bottom five countries according to the percentage of households with access to clean water.

When ranking countries by the number of people living without access to safe water, India comes out worst – 75.8 million people have no access to safe water, followed by China, Nigeria and Ethiopia.

Henry Northover, head of policy for WaterAid, said the global water and sanitation crisis was not a problem of limited supplies.

“This is not always an issue of scarcity – by and large we are dealing with a distributional crisis. It is fixable with clear and coherent government policies, and with the focused support of international agencies. There is perverse irony when it comes to water poverty, those who have the least have to pay the most for this most essential of human needs. And they pay the most not in proportion of their income, but in absolute terms. If you live in a slum in Nairobi, you are paying more in absolute terms for a cubic metre of water than if you were living in Manhattan.” Northover said.

Efforts to make clean water more available have paid off, with 2.6 billion people gaining access since 1990.

Cambodia tops the list of countries with the greatest improvement in increasing access to safe water, followed by Mali, Laos and Ethiopia.